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Incidences reported are based on number of patients/operations rather than nerves at risk a Benign disease only b Total thyroidectomy only c Malignant disease only

Incidences reported are based on number of patients/operations rather than nerves at risk a Benign disease only b Total thyroidectomy only c Malignant disease only ables which affect the comparison of reported studies include the original pathology and the extent of the surgery performed. Most studies agree that the risk of recurrent nerve complications is considerably increased in re-operative surgery, whether for benign or malignant disease [9-11]. Many authors also report a higher incidence of complications with malignant pathology [9-11], hyperthyroidism [12], or Graves disease [10]. It is also clear that identification of the nerve during thyroidectomy decreases the possibility of injury [9,13-15], and routine nerve exposure is to be pursued in every case where this is possible without undue additional tissue dissection. Several intraoperative identification and monitoring techniques have been introduced as adjuncts to this task, but there has been no clear evidence that their routine use results in decrease of the incidence of recurrent nerve injury [16,17]. Their principal utility may lie in cases of higher risk, although even in such instances misleading results may be obtained [18]. It appears that regardless of surgical circumstances, there is no substitute for a thorough familiarity with the anatomy and its variants, precise dissection, and prudence.

The vocal fold may be paralyzed before surgery by primary thyroid disease in as many as 1.2% of patients [19], a factor which argues in favor of routine preoperative evaluation of the larynx. The vocal fold is far more likely to be paralyzed when the underlying thyroid mass is malignant, but the majority of paralyzed vocal folds are caused by benign disease [19, 20]. In these instances, there is a potential for nerve recovery after decompression by thyroidectomy. The presence of vocal fold paralysis in a patient with thyroid carcinoma, even of the well-differentiated variety, is a marker of locally advanced disease and a poor prognostic indicator [21].

Anterior Approach to the Cervical Spine

Anterior exposure of the cervical spine requires separation of the laryngopharyngeal complex from the lateral tissues of the neck, including the carotid sheath. The recurrent nerve is thus necessarily stretched between its vagal origin and its end organ. Because the right-sided nerve is both shorter and has a more oblique trajectory, it is held to be more susceptible to such an injury than the left [22, 23]. The predominance of right-sided lesions (15 of 16) in the series of Netterville et al. seems to be in accord with this [24], but not all series feature such an asymmetrical distribution of cases. An alternate explanation attributes the vocal cord paralysis to endolaryngeal pressure on the terminal branches of the recurrent nerve from the endotracheal tube cuff, which is pressed against the side of the larynx and pulled against the underside of the vocal fold as the larynx is displaced laterally by the Cloward retractor [25]. A simple maneuver consisting of deflating the cuff and repositioning the tube following placement of the retractor was successful in decreasing the incidence of vocal fold paralysis from 6.4 to 1.7%, a difference which was statistically significant.

The incidence of vocal fold paralysis following an anterior approach to the cervical spine may be about 3%, decreasing to 0.3-2.7% over time (Table 3.8). It is interesting that a systematic laryngoscopic assessment of all patients 3-7 days following surgery revealed a surprisingly high incidence of vocal fold paralysis [26], the majority of which was asymptomatic. Approximately 70% of these cases resolved over 3 months. It is possible that many more cases of vocal fold paralysis occur than is generally accepted, and either are asymptomatic or resolve in the period of time during which dysphonia is dismissed as a routine aftereffect of intubation. This course would be expected in a mild traction or compression injury, and may be typical in many scenarios of iatrogenic vocal fold injury. Such findings also underline the effect of the time of evaluation on the incidence of vocal fold injury observed, and this poorly controlled variable should be kept in mind throughout this review.

Dysphagia is not infrequent following this operation, but it is not always due to vocal fold paralysis. Lateral displacement of the laryngopharyngeal complex from the anterior surface of the spine may disrupt the pharyngeal plexus.

Table 3.8. Vocal fold paralysis after anterior approach to the cervical spine

Reference

Year

Number

Temporary (%)

Permanent (%)

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